1. Field of the Invention
This invention relates in general to a cold cathode fluorescent display (CFD) and in particular, to a high luminance, high efficiency, long lifetime, monochrome or multi-color or full-color ultra-large screen display device, which can display character, graphic and video image for both indoor and outdoor applications.
2. Description of the Prior Art
The major prior technologies for ultra-large screen display are as follows:
A. Incandescent Lamp Display:
The display screen consists of a lot of incandescent lamps. The white lamps are always used for displaying the white and black characters and graphics. The color incandescent lamps, which use red, green, and blue (R, G, B) color glass bubbles, are used for displaying multi-color or full-color character, graphic and image. The incandescent lamp display has been widely used for outdoor character and graphic displays and possesses certain advantages such as high luminance, functionable at direct sunlight with shade and low cost of lamps. Nevertheless, this technology suffers from the following disadvantages: low luminous efficiency (i.e., white lamp about 10-12 lm/W; R, G, B.ltoreq.1/3 of white); high power consumption; poor reliability, unexpected lamp failure; short lifetime; expensive maintenance cost; long response time and unsuitable for video display.
B. LED:
LED has been widely used for indoor large screen and ultra-large screen display, to display multi-color and full-color character, graphic and video images. This display is able to generate high luminance for indoor applications and can maintain a long operation lifetime at indoor display luminance level. The disadvantages of LED, however, are as follows: low luminous efficiency and high power consumption especially for the ultra-large screen display; low luminance for outdoor application especially the wide viewing angle is required or at direct sunlight; expensive, especially for ultra-large screen display because the need of a lot of LEDs; and lower lifetime at high luminance level.
C. CRT:
CRT includes Flood-Beam CRT (e.g., Japan Display '92, p. 385, 1992), and matrix flat CRT (e.g., Sony's Jumbotron as disclosed in U.S. Pat. No. 5,191,259) and Mitsubishi's matrix flat CRT (e.g. SID '89 Digest, p. 102, 1989). The CRT display is generally known for its ability to produce good color compatible with color CRT. The disadvantages of CRT are as follows: low luminance for outdoor applications; low contrast at high ambient illumination operating condition; short lifetime at high luminance operating condition; expensive display device due to complex structure and high anode voltage about 10 kv.
D. Hot Cathode Fluorescent Display:
Hot cathode fluorescent technology has been used in a display system called "Skypix" (SED '91 Digest, p. 577, 1991) which is able to generate a high luminance about 5000 cd/m.sup.2 and can be operated at direct sunlight. The disadvantages of this system are: low luminous efficiency due to hot cathode and short gas discharge arc length; very high power consumption and short lifetime because hot cathode and too many switching times for video display.
At present, the incandescent lamps are commonly used for outdoor character and graphic displays.
The matrix flat CRT, including flood beam CRT and matrix CRT, is the most common display for outdoor video display. Neither of these two technologies presents a display system which can be used in both indoor and outdoor applications possessing unique features overcoming all or substantially all of the disadvantages described above.